/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.SortedSet;
import javax.annotation.Nullable;

/**
 * A sorted set which forwards all its method calls to another sorted set. Subclasses should
 * override one or more methods to modify the behavior of the backing sorted set as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>
 * <b>Warning:</b> The methods of {@code ForwardingSortedSet} forward <i>indiscriminately</i> to the
 * methods of the delegate. For example, overriding {@link #add} alone <i>will not</i> change the
 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code addAll} as well, either providing your own implementation, or delegating to the
 * provided {@code standardAddAll} method.
 *
 * <p>
 * <b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingSortedSet}.
 *
 * <p>
 * Each of the {@code standard} methods, where appropriate, uses the set's comparator (or the
 * natural ordering of the elements, if there is no comparator) to test element equality. As a
 * result, if the comparator is not consistent with equals, some of the standard implementations may
 * violate the {@code Set} contract.
 *
 * <p>
 * The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Mike Bostock
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingSortedSet<E> extends ForwardingSet<E> implements SortedSet<E> {

    /** Constructor for use by subclasses. */
    protected ForwardingSortedSet() {}

    @Override
    protected abstract SortedSet<E> delegate();

    @Override
    public Comparator<? super E> comparator() {
        return delegate().comparator();
    }

    @Override
    public E first() {
        return delegate().first();
    }

    @Override
    public SortedSet<E> headSet(E toElement) {
        return delegate().headSet(toElement);
    }

    @Override
    public E last() {
        return delegate().last();
    }

    @Override
    public SortedSet<E> subSet(E fromElement, E toElement) {
        return delegate().subSet(fromElement, toElement);
    }

    @Override
    public SortedSet<E> tailSet(E fromElement) {
        return delegate().tailSet(fromElement);
    }

    // unsafe, but worst case is a CCE is thrown, which callers will be expecting
    @SuppressWarnings("unchecked")
    private int unsafeCompare(Object o1, Object o2) {
        Comparator<? super E> comparator = comparator();
        return (comparator == null) ? ((Comparable<Object>) o1).compareTo(o2)
                : ((Comparator<Object>) comparator).compare(o1, o2);
    }

    /**
     * A sensible definition of {@link #contains} in terms of the {@code first()} method of
     * {@link #tailSet}. If you override {@link #tailSet}, you may wish to override
     * {@link #contains} to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    @Beta
    protected boolean standardContains(@Nullable Object object) {
        try {
            // any ClassCastExceptions are caught
            @SuppressWarnings("unchecked")
            SortedSet<Object> self = (SortedSet<Object>) this;
            Object ceiling = self.tailSet(object).first();
            return unsafeCompare(ceiling, object) == 0;
        } catch (ClassCastException e) {
            return false;
        } catch (NoSuchElementException e) {
            return false;
        } catch (NullPointerException e) {
            return false;
        }
    }

    /**
     * A sensible definition of {@link #remove} in terms of the {@code iterator()} method of
     * {@link #tailSet}. If you override {@link #tailSet}, you may wish to override {@link #remove}
     * to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    @Beta
    protected boolean standardRemove(@Nullable Object object) {
        try {
            // any ClassCastExceptions are caught
            @SuppressWarnings("unchecked")
            SortedSet<Object> self = (SortedSet<Object>) this;
            Iterator<Object> iterator = self.tailSet(object).iterator();
            if (iterator.hasNext()) {
                Object ceiling = iterator.next();
                if (unsafeCompare(ceiling, object) == 0) {
                    iterator.remove();
                    return true;
                }
            }
        } catch (ClassCastException e) {
            return false;
        } catch (NullPointerException e) {
            return false;
        }
        return false;
    }

    /**
     * A sensible default implementation of {@link #subSet(Object, Object)} in terms of
     * {@link #headSet(Object)} and {@link #tailSet(Object)}. In some situations, you may wish to
     * override {@link #subSet(Object, Object)} to forward to this implementation.
     *
     * @since 7.0
     */
    @Beta
    protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
        return tailSet(fromElement).headSet(toElement);
    }
}
